The invention relates to a reflector high-pressure discharge lamp unit in accordance with the features of the preamble of claim 1.
Such a reflector high-pressure discharge lamp unit is disclosed in DE 30 33 688. In this case, a high-pressure discharge lamp and a reflector are permanently connected as an assembly. An electrically insulating first base part is connected to the reflector neck and the lamp, and a second base part, which consists of ceramic and takes the form of a ring, is connected to the light-emitting exit opening of the reflector. The supply lead connected to the end of the lamp situated in the light-exit direction is constructed as a metal band or welded to a metal band running over the cross section. The metal band ends in a free-standing, metallic contact pin, which is fastened on the ring of the base part and serves to make electric contact with the lamp by means of a high-voltage cable.
Furthermore, U.S. Pat. No. 5,506,464 describes a closed reflector discharge lamp arrangement in which the supply lead of the first lamp shank of the discharge lamp, which is arranged with its longitudinal axis on the axis of the reflector, is electrically connected to a first base part made from metal. The end of the first lamp shank is fastened by means of cement in the reflector neck, together with the first base. The supply lead of the end of the lamp shank situated in the light-exit direction is guided outward through the reflector and electrically connected to a free-standing, metallic contact angle fastened on the reflector.
The above-named reflector discharge lamps are preferably used in video and data projectors, that is to say in projection devices in which liquid crystals or DMDs (DMD(trademark)=Digital Mirror Device from Taxas Instruments) are used as light valves. Most recently, it has been chiefly what are termed xe2x80x9cultracompactxe2x80x9d projectors that have been gaining importance here, and in these a high degree of portability is ensured owing to their small external dimensions and compact design, in conjunction with their low weight. High-pressure discharge lamps which are employed in the reflector lamps used require a high-voltage pulse of a few kV for starting, and even several tens of kilovolts in the case of hot starting. Consequently, not only must the two lamp connections be adequately insulated electrically from one another, but the electric connections of the lamp arrangement must also be adequately insulated electrically from the housing part of the projection unit in order to exclude a potential risk to the user, and in order to avoid a short circuit to earth, which could entail destruction of electronic components of the projection unit. In the case of the frequently used, advantageous symmetrical starting, this holds for both electric connections of the lamp, although there is problem, in particular, with the lamp connection of the end of the lamp shank situated in the light-exit direction, since here the diameter of the reflector, and thus also of the overall arrangement, is substantially larger than the diameter of the reflector neck or of the first base. In order to ensure the electrical insulation of the electric connections of the lamp from the housing of the projection unit, it is necessary either to observe appropriately large spacings inside the unit, which conflicts with the desired compactness, or there must be more outlay in the form of additional electric insulations.
It is therefore the object of the present invention to create a reflector high-pressure discharge lamp unit of the generic type in a compact design for use in projection units, in the case of which the shock resistance of the lamp connection of the end of the lamp shank situated in the light-exit direction is ensured in a simple way and the required strain relief of the high-voltage cable is simultaneously created.
The object is achieved by means of the characterizing features of claim 1. Further advantageous refinements of the reflector high-pressure discharge unit are to be gathered from the subclaims.
The required strain relief and high-voltage insulation are achieved by the direct connection of the end of the second supply lead or of the connecting line to the second supply lead to the end of the second high-voltage cable, and the embedding of this connecting region in the second base part, designed as a mechanical auxiliary part, made from electrically non-conducting material.
It is advantageous in this case that the end of the second supply lead or the connecting line to the second supply lead is directly soldered and welded to the end of the second high-voltage cable. Moreover, the end of the second high-voltage cable is embedded in a bore in the edge of the second base part. In order to achieve a still higher degree of high-voltage insulation, the second base part can have a cylindrical appendage on the edge in the region of the bore in order to lengthen the bore. Consequently, a larger section of the end of the high-voltage cable surrounded by insulation can be embedded in the bore, resulting in the achievement of a further increase in the shock resistance. This encapsulation of the connecting point by the high-voltage cable and supply lead or connecting line ensures that at the required high voltages no free-standing metal parts are exposed which could lead to a direct high-voltage flashover (air spark), and all leakage paths are long enough to exclude a surface discharge which could develop into a high-voltage flashover. Selecting the wall thickness of the auxiliary part made from electrically non-conducting material in accordance with the required high voltage additionally prevents high-voltage breakdown, and so when installing the reflector high-pressure discharge lamp unit according to the invention in a projection unit, there is no need to observe any special insulating spacings, nor are additional electric insulations required.
In order to achieve the desired strain relief of the high-voltage cable, the diameter of the bore in the cylindrical appendage should advantageously be equal to, or only slightly larger than, the diameter of the insulating part of the high-voltage cable.
The end of the supply lead remote from the reflector neck, or the end of the connecting line of the supply lead remote from the reflector neck from the end of the bulb shank of the high-pressure discharge lamp to the second base part is advantageously guided in a shockproof groove in the region of the second base part.
In order to be able to introduce the end of the high-voltage cable and the end of the second supply lead or the end of the connecting line into the bore or groove on the second base part in the connected state, the cylindrical appendage is advantageously provided in the region of the bore with a slot which runs parallel to the bore and reaches up to the groove.
The high-voltage cable can also advantageously be fixed in the bore by means of a screw made from insulating material, in order to achieve an even higher degree of strain relief.
In this case, the bore advantageously runs parallel to the axis of the high-pressure discharge lamp, and thus also parallel to the axis of the reflector. This keeps as small as possible the space required in the projection unit for the reflector high-pressure discharge lamp unit.
In order to pass radiation/light, the second base part, designed as an auxiliary part, respectively has an aperture on the side respectively facing and averted from the radiation/light exit of the reflector. It is advantageously permanently connected to the reflector. For reasons of safety, the second aperture of the auxiliary part is advantageously sealed with a face-plate transparent to radiation/light. This prevents combustible objects from touching hot lamp parts. In the case of an explosion of the high-pressure discharge lamp, this face-plate, in addition, protects sensitive optical components in the unit from damage. Moreover, the face-plate constitutes an additional electrical insulation of the end of the second lamp shank of the discharge lamp situated in the light-exit direction, and the supply lead thereof, and so the overall length in the light-exit direction can be kept compact. The face-plate can be fastened on the auxiliary part with the aid of an adhesive, for example a silicone adhesive, or be held in position mechanically by clamps or a ring.
If required, the auxiliary part can additionally be provided with one or more lateral openings in order to use a specifically controlled air flow to cool thermally critical sites such as, for example, the end of the second lamp shank of the discharge lamp situated in the light-exit direction, in the case of combination with an elliptical reflector.
A precisely adjusted installation of the lamp in an optical unit, in particular a video and/or data projector, is advantageously facilitated by fitting reference points and threaded holders on the second base part.
If the second base part designed as auxiliary part is produced from an injection moldable high-temperature plastic, this has the advantage by comparison with other materials such as, for example, ceramics that a high measure of flexibility exists with reference to the configuration of the geometrical shape of the auxiliary part, and that a lower weight is achieved. The use of glass fiber reinforced plastic additionally advantageously enhances the mechanical stability of the auxiliary part. The material PEEK(trademark) (polyether ether ketone) has proved to be particularly advantageous as injection moldable high-temperature material, since it has a very high thermostability and a good UV compatibility.